In medicine, there is currently a multiplicity of different methods of examining tissue for the presence of benign or malignant changes, without having to remove tissue itself in connection with a biopsy that is often very unpleasant for a patient. One of the most frequently employed methods consists in recording and analyzing X-ray images, which usually requires the patient to be injected with a contrast medium. Although X-ray analysis is one of the safest methods, it does expose the patient to a high radiation dose, which may itself, under certain conditions, produce lesions in the tissue by ionization. Therefore, it has been attempted to keep the radiation exposure to a minimum. For example, the dosage of approximately 0.7 Millisievert used in classic mammography is relatively low.
Not least due to the fact that X-rays burden the human organism, other methods of examination have also been developed further over the last few decades, in addition to classic X-ray analysis, such as, for example, ultrasonic analysis, computer tomography, magnetic resonance examinations as well as, based upon the latter, the so-called Magnetic Resonance Imaging (MRI), which used to be referred to also as Magnetic Resonance Tomography (MRT) or Nuclear Magnetic Resonance (NMR). MRI, in particular, has been continuously developed further over the past few years and has proven to be a method excellently suited to represent living organisms. In medicine, MRI is preferably used to image pathological or other physiological changes in tissue.
The analysis of the images—be they X-ray images or MR images—is then usually the responsibility of the physicians in charge. Whether a benign or malignant tissue change is present is assessed by the presence or absence, respectively, of various kinetic or morphological signs or patterns, respectively. In a broader sense, clinical data—such as, for example, serological findings or fever values—can be additionally taken into consideration. Thus, the evaluation of the images and data is strongly dependent on the experience of the physician or physicians. To aggravate the situation, many of the signs or tissue patterns appear in variations, being more pronounced in some patients and less pronounced in others, sometimes not being present at all. This has lead to misdiagnoses time and time again, in particular when analyzing images obtained by the not yet generally established MRI method of examination. For example, in mammography approximately ten to twenty percent of malignant tissue changes are not identified as such. On the other hand, benign tumors are sometimes also mistaken for malignant ones, in the worst case resulting in unjustified removal of a breast in such patients.
Since breast cancer is the second-most frequent cancer-related cause of death in women, there is an ongoing search for ways to avoid such errors as far as possible and/or to reduce the risk of misdiagnoses. In this context, computer aided diagnosis (CAD) plays an important role. Digitized X-ray images, MR images, etc. of tissue are analyzed by image-processing algorithms as to whether certain features, i.e. patterns of signs, can be recognized in the image. If the image-processing software recognizes such features, it will mark them, for example, by highlighting them graphically, thus pointing out these specific regions in the image to the physician looking at the image. It is also the sole responsibility of the physician to decide how the sites found by the image-processing program will be evaluated. Thus, the risk of wrong decisions is not excluded here either, but merely somewhat reduced. Programs capable of learning—such as neuronal networks, for example—are used in an attempt to further reduce these sources of error. In addition, increasingly large databases, such as those of the European MammoGrid project, are being generated so that an ever-increasing set of data is available for CAD. However, the disadvantage still remains that, in the end, a subjective evaluation by the physician decides how the conspicuous phenomena observed by himself and those detected by the program are to be evaluated and whether further steps, such as a biopsy or an operation, are necessary.